[TypeScript] The return type of drive.files.get is inferred wrongly when downloading as media

[TonalidadeHidrica]

The following is a small snippet to download a file from Google Drive using this API.

import {createDriveClient} from "./utils";
import fs from "fs";
import * as stream from "stream";
import {promisify} from "util";

(async () => {
    const drive = await createDriveClient();
    const {data} = (await drive.files.get({
        fileId: "anyFileId",
        alt: "media",
    }, {responseType: "stream"})) as unknown as { data: stream.PassThrough };
    const out = fs.createWriteStream("destinationFile");
    await promisify(stream.pipeline)(data, out);
})().catch(console.error);

The problem is that drive.files.get is defined to be returning (primarily) GaxiosPromise<Schema$File> according to the type definitions around here. However, when alt: "media" is specified, the method returns string (by default) or stream.PassThrough (when {responseType: "stream"}, or maybe other various types.

Therefore, when I try to use the API with TypeScript properly, I have to apply an ugly cast ( as unknown as { data: stream.PassThrough } to the response of the function. Can it be improved?

[JustinBeckwith]

This is a real bug. Step 1 is to land this PR and cut a release:
googleapis/nodejs-googleapis-common#283

Next, we need to add method signature overloads to the generator that look like this:

    get(
      params?: Params$Resource$Sites$Get,
      options?: MethodOptions
    ): GaxiosPromise<Schema$SiteSummaryResponse>;
    get(
      params?: Params$Resource$Sites$Get,
      options?: StreamMethodOptions
    ): GaxiosPromise<Readable>;
    get(
      params: Params$Resource$Sites$Get,
      options: MethodOptions | BodyResponseCallback<Schema$SiteSummaryResponse>,
      callback: BodyResponseCallback<Schema$SiteSummaryResponse>
    ): void;
    get(
      params: Params$Resource$Sites$Get,
      options: StreamMethodOptions | BodyResponseCallback<Readable>,
      callback: BodyResponseCallback<Readable>
    ): void;
    get(
      params: Params$Resource$Sites$Get,
      callback: BodyResponseCallback<Schema$SiteSummaryResponse>
    ): void;
    get(callback: BodyResponseCallback<Schema$SiteSummaryResponse>): void;
    get(
      paramsOrCallback?:
        | Params$Resource$Sites$Get
        | BodyResponseCallback<Schema$SiteSummaryResponse>
        | BodyResponseCallback<Readable>,
      optionsOrCallback?:
        | MethodOptions
        | StreamMethodOptions
        | BodyResponseCallback<Schema$SiteSummaryResponse>
        | BodyResponseCallback<Readable>,
      callback?: BodyResponseCallback<Schema$SiteSummaryResponse> | BodyResponseCallback<Readable>
    ): void | GaxiosPromise<Schema$SiteSummaryResponse> | GaxiosPromise<Readable> {